The present invention relates to a method and apparatus for testing a composite type magnetic head which has a read head portion with a magnetoresistive effect (MR) element for reproducing data from a magnetic medium such as a magnetic disk, and a write head portion with an inductive element for recording data into the magnetic medium.
The composite type magnetic heads described above have been broadly utilized as thin-film magnetic heads for reading data from and/or writing data into the magnetic medium such as the magnetic disk. Recently, a magnetic head with a giant magnetoresistive effect (GMR) element such as a spin-valve MR element or with a tunnel magnetoresistive effect (TMR) element has been developed to increase magnetic recording density, instead of a usual magnetic head with an anisotropic magnetoresistive effect (AMR) element.
At each test after manufacturing such magnetic head, it is necessary to confirm that the finished magnetic head with a MR element is a good article and may not produce any inherent noise such as Barkhausen noise. Japanese Patent Unexamined Publication No.6 (1994)-150264 of the same assignee as that of the present application discloses a MR head testing method. In this testing method, an external alternating magnetic field is applied, in a direction perpendicular to an Air Bearing Surface (ABS), to a plurality of MR heads which are aligned on a head block and are not yet individually separated, and electromagnetic transfer characteristics of each of the MR heads under the varying external magnetic field is measured. By means of this conventional testing method, whether Barkhausen noise is produced or not can be easily checked.
U.S. Pat. No. 5,721,488 of the same assignee as that of the present application discloses an improved MR head testing method. In this testing method, alternating leakage magnetic field with a high frequency excited by a write current flowing through an inductive element is applied to the MR element in addition to external alternating magnetic field which is applied to the MR element in a direction perpendicular to the ABS of the head block, and electromagnetic conversion characteristics of each of the MR heads under the varying external and leakage magnetic fields is measured. By means of this testing method disclosed in U.S. patent, possible Barkhausen noise can be detected with a high probability.
These known testing methods using the electromagnetic conversion characteristics measuring device can be used for detecting whether Barkhausen noise is produced or not but cannot be applied for detecting instability of output of the MR element, which is different from abnormal output of the MR element due to Barkhausen noise. In fact, when outputs of the MR element of the composite type magnetic head are repeatedly measured by means of the electromagnetic conversion characteristics measuring device, the output wave shapes of the MR element sometimes vary due to some reason and thus the same output level cannot be always obtained resulting poor reproducibility.
Therefore, according to the conventional testing method, it is impossible to detect instability of output of the MR element except that extremely many times of the test are repeated to increase the probability of the detection. However, the great number of the repetition times of the test will invite manufacturing efficiency of the head to extremely lower.
Particularly, the composite type magnetic head with the GMR element or the TMR element may easily trigger the output instability because such magnetic head has high sensitivity and complicated structure and therefore is susceptible to its environment.
It is therefore an object of the present invention to provide a method and apparatus for testing a composite type magnetic head, whereby easy and reliable test with respect to instability of output of a MR element can be attained.
According to the present invention, a method for testing a composite type magnetic head having a MR element with at least one shield layer and an inductive element include a current application step of applying a current to the inductive element, which current will change an initial magnetization state of the shield layer for the MR element, and a measurement step of measuring output characteristics of the MR element.
Also, according to the present invention, an apparatus for testing a composite type magnetic head having a MR element with at least one shield layer and an inductive element, includes a first current application means for applying a current to the inductive element, which current will change an initial magnetization state of the shield layer for the MR element, a second current application means for applying a sense current to the MR element, and measurement means for measuring output characteristics of the MR element by receiving output voltage from the MR element each time the current is applied to the inductive element from the first current application means while the sense current is flowing.
Furthermore, according to the present invention, an apparatus for testing a composite type magnetic head having a MR element with at least one shield layer and terminals, having an inductive element with terminals, and having an air bearing surface, include probe means for electrically contacting to the terminals of the MR element and to the terminals of the inductive element, a first current application means for applying a current to the inductive element through the probe means, which current will change an initial magnetization state of the shield layer for the MR element, means for applying external magnetic field to the magnetic head, the external magnetic field being perpendicular to the air bearing surface, a second current application means for applying a sense current to the MR element through the probe means, and measurement means for measuring output characteristics of the MR element by receiving output voltage from the MR element through the probe means each time the current is applied to the inductive element from the first current application means while the sense current and the external magnetic field are being applied.
The current which will change an initial magnetization state of the shield layer for the MR element is applied to the inductive element, and output characteristics of the MR element is measured. According to the present invention, output characteristics of the MR element is not merely measured but is measured under a condition wherein possible instability of the output of the MR element will be intentionally induced by forcefully applying to the inductive element a current which will change an initial magnetization state of a shield layer for the MR element. It is impossible to increase the probability of detection of instability of output of the MR element only by applying a high frequency write current to the inductive element as done in the conventional art. By applying current which will change an initial magnetization state of the shield layer for the MR element is applied to the inductive element as the present invention, possible output instability will be easily induced. Thus, according to the present invention, possible output instability of the MR element can be tested without increasing the number of the repetition times of the test.
It is preferred that the applied current is a direct current with a predetermined polarity, and that output characteristics of the MR element is measured while the applied direct current is flowing.
It is also preferred that the applied current is a current which finally falls to zero from a predetermined polarity to the inductive element, and that output characteristics of the MR element is measured after application of the current is finished.
According to the present invention, furthermore, a method for testing a composite type magnetic head having a MR element and an inductive element, includes a first current application step of applying a first current with one polarity to the inductive element, a first measurement step of measuring output characteristics of the MR element, a second current application step of applying a second current with the other polarity to the inductive element, and a second measurement step of measuring output characteristics of the MR element.
Also, according to the present invention, an apparatus for testing a composite type magnetic head having a MR element and an inductive element, includes a first current application means for applying a first current with one polarity and a second current with the other polarity to the inductive element, a second current application means for applying a sense current to the MR element, and measurement means for measuring output characteristics of the MR element by receiving output voltage from the MR element when the first current is applied to the inductive element from the first current application means while the sense current is being applied, and for measuring output characteristics of the MR element by receiving output voltage from the MR element when the second current is applied to the inductive element from the first current application means while the sense current is being applied.
According to the present invention, also, an apparatus for testing a composite type magnetic head having a MR element with at least one shield layer and terminals, having an inductive element with terminals, and having an air bearing surface, includes probe means for electrically contacting to the terminals of the MR element and to the terminals of the inductive element, a first current application means for applying a first current with one polarity and a second current with the other polarity to the inductive element through the probe means, means for applying external magnetic field to the magnetic head, the external magnetic field being perpendicular to the air bearing surface, a second current application means for applying a sense current to the MR element through the probe means, and measurement means for measuring output characteristics of the MR element by receiving output voltage from the MR element through the probe means when the first current is applied to the inductive element from the first current application means while the sense current and the external magnetic field are being applied, and for measuring output characteristics of the MR element by receiving output voltage from the MR element through the probe means when the second current is applied to the inductive element from the first current application means while the sense current and the external magnetic field are being applied.
The output characteristics of the MR element is detected when a current with one polarity is applied to the inductive element, and the output characteristics of the MR element is detected when a current with the other polarity is applied to the inductive element. As mentioned before, according to the present invention, output characteristics of the MR element is measured under a condition wherein possible instability of the output of the MR element will be intentionally induced by forcefully applying to the inductive element a current which will change an initial magnetization state of a shield layer for the MR element. However, since it is impossible to previously know that, for each MR element, which polarity of the applied current will change the initial magnetization state of the shield layer, the output characteristics of each MR element should be measured by using a plurality of currents with positive and negative polarities, respectively. Thus, at least twice measurements each applying a current with different polarity to the inductive element are executed.
It is preferred that the first and second currents are direct currents, and that output characteristics of the MR element is measured while the applied direct currents are flowing, respectively.
It is also preferred that the first current finally falls to zero from one polarity to the inductive element, that the second current finally falls to zero from the other polarity to the inductive element, and that output characteristics of the MR element is measured after application of the first and second currents are finished, respectively.
In the latter case, each of the first and second currents may be a single rectangular wave shape current with a predetermined duration, an alternating rectangular wave shape current with a predetermined frequency, or a sinusoidal wave shape current with a predetermined frequency.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.